With this week’s unexpected release of veteran Stanford Routt, who was signed as a high-dollar free agent to replace the even bigger-dollar departure of Brandon Carr, Arenas has shifted from his nickel back spot and sits squarely on the pressure-packed position of right corner.

“It’s a different monster out there,” Arenas said of moving from covering slot receivers to taking on the primary receivers on the outside. “I’ve been in the NFL for three years. … I can get it done. I know I can. It’s not like I’ve never played on the outside before. I’m excited about this opportunity.”

In his only start last season, Arenas, as the nickel back, matched up against New England’s slot receiver, Wes Welker, and held the NFL’s receptions leader to two catches for 22 yards, though the Chiefs lost 34-3.

“I’ve had some of the best receivers in the slot on third down,” Arenas said. “They come in there sometimes, too. It’s not going to be brand new …”

Playing on the outside, Arenas, who stands 5-foot-9, will be taking on some taller and faster receivers. Last Thursday night at San Diego, when Arenas started in place of the injured Routt, he was beaten on consecutive plays for gains of 16 and 12 yards by San Diego’s Malcom Floyd, who is 6-foot-5.

“He’s a great receiver, but you have to control those guys, get your hands on those guys, and if you play off (in a zone), you have to play the right technique,” said Arenas, a second-round draft pick from Alabama in 2010. “The other night was my first go-around; I got a good feel, I got a chance to get out there …

“I had a couple of balls caught on me and had a chance to come up and make a couple of tackles. I got my feet wet. It’s the NFL. Those guys are going to make plays, too. I just want to dive in and do all they ask of me and play to the best of my ability.”

Opponents tend to attack the Chiefs’ right cornerback and nickel back because of the presence of Brandon Flowers on the left side. With Arenas starting in place of Routt last week, Travis Daniels moved into the nickel spot and was beaten handily by the Chargers’ Danario Alexander, the University of Missouri product who was playing in just his second game with San Diego.

“Wouldn’t you?” Arenas said of teams picking on the right side. “It’s a spot where you’ve had guys in and out. You had a great guy in Carr there, you had a real good corner in Routt, and now you’re going at me.

“Flowers is an outstanding cornerback (who has) proven himself year-in and year-out. You have to look for the weak points in the defense from your perspective, which would be the other side.”

Statistics could bear that out. According to Pro Football Focus, teams completed 25 of 39 passes against Routt (64 percent) for 491 yards and three touchdowns. Of those 491 yards, 267 came after the catch, highlighted by a spectacular 62-yard catch and run by Tampa Bay’s Mike Williams.

Meanwhile, quarterbacks have completed 72 percent of their passes against Arenas with a whopping 137.3 passer rating, according to Pro Football Focus.

It may be that Chiefs coach Romeo Crennel made the change because of what happens after the catch rather than merely receptions.

“He’s a very competitive player,” Crennel said of Arenas’ play at San Diego. “He was off a little bit too far at times, and they completed a couple balls in front of him, but he made tackles. He came up on the run support and made tackles on the run support, so I think he represented himself pretty decently.”

Monday night’s opponent, the Pittsburgh Steelers, features two of the most dangerous and speediest wide receivers in the NFL, in Antonio Brown (42 receptions, 499 yards, one touchdown) and Mike Wallace (39-525-5, including an 82-yard TD). Brown’s status for the game is in doubt — he has an ankle injury — but Wallace, a 2011 Pro Bowl starter, averaged 21.0 yards per reception on 60 catches in 2010, and 16.6 yards on 72 catches last year.

Arenas squared off against Wallace, who played at Ole Miss, three times in college, so he knows what kind of size (6-foot) and speed he’s going against on Monday.

“I guarded him on a go route, and I was running with him, and I felt his speed,” Arenas said. “The ball was underthrown, so he had to slow down a little bit, and I made a play on the ball. So I do understand his speed.”

Unlike in college, Wallace doesn’t have to worry about too many underthrown passes from Steelers quarterback Ben Roethlisberger.

“With a different-caliber quarterback throwing to him, that makes a huge difference, of course,” Arenas said, “because if he has two steps on a guy, he’s not slowing down for that football. But I covered him last year … I covered the other guys last year playing against them. It’s a different game, a new year, but this isn’t a new walk for me.”

Arenas, who has been the Chiefs’ primary punt returner this season and ranks ninth in the NFL with a 10.0-yard average, hopes to maintain that job, even though he’ll be playing full-time on defense.

“I think it will help me more on returns,” he said. “Being out there, playing that position will give me a good opportunity to get into the game. I’ll be warm going out there.”

I wont pass judgement on brown until the end of this year. I knew him in college and he is a smart guy off the field. Hes a great special teamer, maybe not a star starting corner but he could be our serviceable backup for a few years. I hope he continues to get better. I know for a fact he is trying his hardest every day